Biomedical subjects

J Schlaier

Publications and source records attributed to J Schlaier.

14 recordsLinked to original sources

PubMed2005

Reliability of atlas-derived coordinates in deep brain stimulation.

BACKGROUND: In deep brain stimulation the way to define and localize the optimal target for the individual patient is still under debate. The objective of our study was to investigate the reliability of atlas derived data by comparing them with direct targeting on MR images. METHOD: We investigated 28 STN targets in 14 volunteers. The stereotactic coordinates of the dorso-lateral subthalamic nucleus (STN), were determined in 5 different ways for both STNs of each individual volunteer: 1. directly, on axial T2WI spin echo slices, 2. directly, on coronal T2WI spin echo slices and after fusion of data sets: 3. indirectly, on an axial atlas plate, 4. indirectly, on a coronal atlas plate, 5. indirectly, 12 mm lateral, 3 mm posterior and 3 mm inferior to mid-AC-PC. FINDINGS: The differences between MRI derived targets on axial vs. coronal slices were not statistically significant. After detection of the atlas derived targets the resulting x-coordinates were found more lateral than after direct detection on both, axial and coronal T2-weighted images (p < 0.001). On axial images y-coordinates were located more anterior (p = 0.240) on atlas derived targets and more posterior when target localizations were compared on coronal slices (p < 0.001). z-Coordinates were more superior after atlas targeting compared to MRI targeting (p < 0.001). Differences up to 6.21 mm occurred. CONCLUSIONS: Despite the limitations concerning image distortions and slice thickness, direct target planning on MRI, regarding our results, is more reliable than targeting solely based on atlas derived data. Only MRI gives us detailed information about the individual configurations of central structures in every single patient. However, targets, which are not detectable on MRI like the nucleus ventralis intermedius have to be planned using stereotactic atlas information. In these cases intra-operative micro-electrode recording might help to better define the target region.

Adult↗

PubMed2005

[Diffusion-weighted imaging in the diagnostic evaluation of the hydrocephalus in patients with acute or chronic increase in cerebral pressure].

PURPOSE: To investigate whether diffusion-weighted imaging (DWI) in magnetic resonance imaging (MRI) provides additional information about the periventricular white matter for the assessment of hydrocephalus. MATERIALS AND METHODS: Sixteen MRI examinations (11 with acutely increased cerebral pressure, 5 without symptoms) on 15 patients with hydrocephalus (4 patients with communicating hydrocephalus and 11 patients with obstructive hydrocephalus) were analyzed. One symptomatic patient subsequently became asymptomatic. We investigated the "apparent diffusion coefficient" (ADC) in the subcortical and periventricular white matter. The ADCs of the study patients were compared with those of a healthy control group. RESULTS: Symptomatic patients with hydrocephalus, 6/11 showed periventricular edema and a significantly higher ADC values in the periventricular region than in the subcortical white matter. 5/11 symptomatic patients showed significantly higher ADC values even in the absence of periventricular interstitial edema (both groups contained patients with communicating and obstructive hydrocephalus). All 5 asymptomatic patients with hydrocephalus did not have a significantly higher ADC values in the periventricular region. CONCLUSION: In patients with hydrocephalus and acutely increased cerebral pressure, DWI showed a significantly higher ADC values in the periventricular region even without visible interstitial edema on conventional MRI sequences.

Adolescent↗

PubMed2005

Diffusion-weighted imaging with calculated apparent diffusion coefficient of enhancing extra-axial masses.

BACKGROUND AND PURPOSE: Sometimes intracranial contrast-enhancing tumors like meningiomas, metastases, lymphomas, and schwannomas can mimic each other. It was the aim of the present study to investigate if intracranial contrast-enhancing lesions can be reliably differentiated with the help of diffusion-weighted imaging with calculated apparent diffusion coefficients (ADCs). METHODS: 29 patients (ages ranging from 22 to 82 years, mean age of 58.6 years) were included. Nine meningiomas, 7 metastases, 6 lymphomas, and 7 schwannomas were investigated. The ADC value in the lesions and in the perifocal edema was analyzed. RESULTS: For the lymphomas, the authors measured the lowest ADC values in the contrast-enhancing part (0.59 +/- 0.09 . 10(-3) mm2/sec). The meningiomas showed a mean ADC value of 0.98 +/- 0.18 . 10(-3) mm2/sec. The schwannomas and metastases showed higher ADC values of 1.33 +/- 0.28 . 10(-3) mm2/sec and 1.05 +/- 0.20 . 10(-3) mm2/sec. The authors saw a statistically significant difference between lymphomas, meningiomas, and metastases concerning the ADC values in the contrast-enhancing part. CONCLUSIONS: In spite of a small sample size and partly a wide range of values, the authors found statistically significant differences between meningiomas, metastases, and lymphomas concerning ADC values. Nevertheless, a differentiation of these lesions only with the help of ADC values seems questionable.

Adult↗

PubMed2004

Degenerative diseases of the cervical spine: comparison of a multiecho data image combination sequence with a magnetisation transfer saturation pulse and cervical myelography and CT.

Assessing degenerative disease in the cervical spine remains a challenge. There is much controversy about imaging the cervical spine using MRI. Our aim in this prospective study was to compare a T2*-weighted 2D spoiled gradient-echo multiecho sequence (MEDIC) with a magnetisation transfer saturation pulse with cervical myelography and postmyelographic CT. Using an assessment scale we looked at the vertebral bodies, intervertebral discs, neural foramina, anterior and posterior nerve roots, grey matter, ligamentaflava, oedema in the spinal cord and stenosis of the spinal canal. We also evaluated postmyelography CT and the MEDIC sequence for assessing narrowing of the neural foramina in a cadaver cervical spine. We examined 67 disc levels in 18 patients, showing 18 disc prolapses and 21 osteophytes narrowing the spinal canal or the neural foramina. All MRI studies showed these abnormalities findings equally well. Postmyelography CT was significantly better for showing the bony structures and the anterior and posterior nerve roots. The MEDIC sequence provided excellent demonstration of soft-tissue structures such as the intervertebral disc and ligamentum flavum. No statistical differences between the imaging modalities were found in the assessment of narrowing of the neural foramina or the extent of spinal stenosis. The cadaver measurements showed no overestimation of abnormalities using the MEDIC sequence.

Adult↗

PubMed2003

Diffusion-weighted echo-planar MRI of the brain with calculated ADCs: a useful tool in the differential diagnosis of tumor necrosis from abscess?

BACKGROUND AND PURPOSE: It was the aim of this study to evaluate whether brain abscesses could be distinguished reliably from necrotic brain tumors using diffusion-weighted imaging (DWI) with calculated apparent diffusion coefficients (ADCs). METHODS: The authors studied 27 lesions in 26 patients (21 tumors and metastases, 5 pyogenic brain abscesses, and 1 cerebral toxoplasmosis). DWI was obtained with a single-shot echo-planar imaging spin-echo sequence. ADCs were calculated for all images. RESULTS: ADCs (x 10(-3) mm2/s) measured in the necrotic parts of the tumors ranged from 2.94 (glioblastoma) to 1.51 (astrocytoma III). In the inflammatory lesions, ADCs ranged between 0.91 and 3.07 (cerebral toxoplasmosis and pyogenic abscess). The contrast-enhanced parts of the lesions showed ADC values from 0.77 (pyogenic abscess) up to 1.68 (glioblastoma). CONCLUSIONS: DWI with calculated ADC values does not allow the reliable differentiation of enhanced central necrotic intracranial lesions.

Astrocytoma↗

PubMed2002

Registration accuracy and practicability of laser-directed surface matching.

The aim of our study was to evaluate the registration accuracy and practicability of a new laser registration technique in comparison to marker registration. From January to August 2001, 36 patients (23 male, 13 female) with brain lesions were operated with navigational guidance. Thirty-five patients were registered by paired-point registration. In 16 patients, a second registration was carried out using a special laser pointer for surface matching (z-touch trade mark, BrainLab, Heimstetten, Germany). Accuracy was evaluated by touching seven anatomic landmarks and a target fiducial with the nonsterile pointer. The distance from the virtual pointer tip to these points was determined on the monitor display (600% zoom). Laser registration is fully retrospective and allows registrations when no markers are applied. z-touch trade mark registration is more sophisticated and time-consuming than marker-based registration (registration time for z-touch trade mark = 7.4 +/- 3.7 min; for markers = 4.1 +/- 1.7 min; p < 0.005). Marker registration proved to be more accurate than z-touch trade mark registration with regard to localization of anatomical landmarks and target fiducials (precision with z-touch trade mark = 2.77 +/- 1.64 mm; with markers = 1.31 +/- 0.87 mm; p < 0.01). Although the registration error was increased and preparation time prolonged with the z-touch trade mark technique, it proved to be a valuable option, especially in children.

Adolescent↗

PubMed2001

Comparison between magnetic resonance phase contrast imaging and transcranial Doppler ultrasound with regard to blood flow velocity in intracranial arteries: work in progress.

OBJECTIVE: The authors evaluate blood flow velocities in the medial cerebral artery (MCA) and the basilar artery using magnetic resonance (MR) phase contrast technique in comparison with transcranial Doppler ultrasound (TCD). Eleven healthy male volunteers were studied. TCD of the MCA (n = 22) and basilar artery (n = 11) was performed. MR phase velocity mapping was done in each vessel at the same location where the TCD signal had been acquired. A 2-dimensional FLASH sequence with retrospective cardiac gating and an average temporal resolution of 45 ms was used. Resistance indices (RIs) and pulsatility indices (PIs) were calculated for both modalities. The TCD insonation angle was measured retrospectively with MR, and TCD velocities were corrected based on these measurements. The comparison of flow velocities obtained with TCD and MR led to a low correlation coefficient with regard to the basilar artery and the MCA: maximum systolic velocity, r = 0.02 and r = 0.50, respectively; enddiastolic velocity, r = 0.47 and r = 0.65, respectively; mean velocity, r = 0.52 and r = 0.66, respectively. The average PIs in the basilar artery and the MCA were 0.80 and 0.81 with MR and 0.65 and 0.85 with TCD, respectively. The average RIs in the basilar artery and the MCA were 0.52 and 0.54 with MR and 0.52 and 0.55 with TCD, respectively. The TCD insonation angle differed significantly from the ideal value in the basilar artery (mean value = 32.6 degrees) and the MCA (mean value = 26.5 degrees). The authors find a low correlation between velocities measured with MRI and TCD but similar results with regard to the PIs and RIs. Several sources of error, such as a nonideal TCD insonation angle, were identified.

Adult↗

PubMed1999

Functional MR imaging of the motor cortex in healthy volunteers and patients with brain tumours: qualitative and quantitative results.

The purpose of this study was to compare functional magnetic resonance (MR) imaging of the motor cortex in healthy volunteers and patients with brain tumours. Functional MR imaging was performed in 14 healthy volunteers and 14 patients with tumours in or near the primary motor cortex with groups being matched for age, sex, and handedness. Functional images were acquired during motion of the right and left hand. Time courses of signal intensity within the contralateral, ipsilateral, and supplementary motor cortex as well as z-maps were calculated, their quality being assessed visually. Mean signal increase between activation and rest were evaluated within the contralateral, ipsilateral, and supplementary motor cortex, the activated area in those regions of interest was measured using z-maps. The quality of functional MR experiments was generally lower in patients than in volunteers. The quantitative results showed a trend towards increased ipsilateral activation in volunteers during left hand compared to right hand motion and in patients during motion of the affected compared to the non-affected hand. Considering quantitative and qualitative results, significantly increased ipsilateral activation was found in patients compared to healthy volunteers. In conclusion, functional MR imaging quality was significantly reduced in patient studies compared to healthy volunteers, even if influences of age, sex, and handedness were excluded. Increased ipsilateral activation was found in patients with brain tumours which can be interpreted by an improved connectivity between both hemispheres.

Adult↗

PubMed1998

Functional MRI of the motor cortex using a conventional gradient system: comparison of FLASH and EPI techniques.

Gradient echo (GE) and echo planar imaging (EPI) techniques are two different approaches to functional MRI (fMRI). In contrast to GE sequences, the ultra short EPI technique facilitates fMRI experiments with high spatial and temporal resolution or mapping of the whole brain. Although it has become the method of choice for fMRI, EPI is generally restricted to modern scanners with a strong gradient system. The aim of our study was to evaluate the applicability of EPI for fMRI of the motor cortex using a 1.5 T scanner with a conventional gradient system of 10 mT/m (rise time: 1 ms). Therefore, EPI was compared with a well-established high-resolution fast low-angle shot (FLASH) technique (matrix size 1282). The FLASH technique was applied additionally with a 64(2) matrix size to exclude influences caused by different spatial resolution, because the EPI sequence was restricted to a 64(2) matrix size. A total of 35 healthy volunteers were included in this study. The task consisted of clenching and spreading of the right hand. FLASH and EPI techniques were compared regarding geometric distortions as well as qualitative and quantitative fMRI criteria: Mean signal increase between activation and rest and the area of activation were measured within the contralateral, ipsilateral, and supplementary motor cortex. The quality of subtraction images between activation and rest, as well as the quality of z-maps and time course within activated regions of interest, was evaluated visually. EPI revealed significant distortions of the anterior and posterior brain margins; lateral distortions (relevant for the motor cortex) could be neglected in most cases. The mean signal increase was significantly higher using FLASH 1282 compared to FLASH 64(2) and EPI 64(2), whereas the activated areas proved to be smaller in FLASH 1282 functional images. Both results can be explained by well-documented partial volume effects, caused by different voxel size. Similar quality of the subtraction images and of the time courses in different regions of interest were found for all techniques under investigation, but slightly reduced quality of z-map in FLASH 1282. Within the limits of reproducibility and measurement accuracy, the location of contralateral activation was similar using FLASH and EPI sequences. In conclusion, EPI proved to be a reliable technique for fMRI of the motor cortex, even on an MR scanner with a conventional gradient system.

Adult↗

PubMed1998

Are there differences in the symptoms, signs and outcome after lumbar disc surgery in the elderly compared with younger patients?

Age is claimed by several authors to be a predictor of bad outcome after lumbar disc surgery. The aim of this study is to evaluate the influence of the patients age on preoperative symptoms and the outcome. General data, symptoms, signs and neurological findings of 219 patients were recorded preoperatively Ninety-two per cent of the patients received a follow-up examination by an independent investigator after a mean of 298 days. All patients older than 59 years were defined as belonging to the group of elderly patients (n = 30). The other patients were defined as the younger group (n = 189). The outcome was measured by a visual analogue rating scale. Outcome was not statistically different in both groups. In our opinion, the indications for surgery for a lumbar disc herniation should be no different for older patients even though nerve root tension signs appear to be less marked in older patients.

Adult↗

PubMed1998

Short-term prognostic factors in lumbar disc surgery: the low back prognostic score is of predictive value.

In order to determine prognostic factors of lumbar disc surgery, we examined 107 patients who were conventionally operated on in a prospective, consecutive study. We analysed general data, the case history, the neurological examination at admission and all data from imaging examinations and therapy. In addition, all patients received a questionnaire based on the Low Back Outcome Score [9, 10]. The patients were re-examined after 2-8 months (103 days mean). According to their ratings on a pain grading scale, the patients were divided into a group with favorable and another with unfavorable results. These groups were analysed in relation to the patients' initial condition. At follow up, 88% of the patients had either completely recovered or their complaints had been relieved. According to the Low Back Outcome Score (LBOS), 64.5% went well. Used to evaluate the initial condition of the patients on admission the LBOS was able to predict favorable outcome in 68% and unfavorable outcome in 50%. To improve the prognostic value, we combined significant questions of the LBOS with the pain grading scale and significant prognostic factors to form a new prognostic score (Low Back Prognostic Score). With this new score we were able to predict a favorable outcome in 84% of our patients, and an unfavorable outcome in 71%. The Low Back Prognostic score seems to provide a sensitive method for predicting a favorable or unfavorable outcome for patients scheduled to undergo lumbar disc surgery.

Adolescent↗

PubMed1997

Cerebral CT angiography in the diagnosis of acute subarachnoid hemorrhage.

PURPOSE: To evaluate the usefulness of CT angiography (CTA) in the detection of intracranial aneurysms in patients with acute subarachnoid hemorrhage (SAH). MATERIAL AND METHODS: In 53 patients with nontraumatic SAH a helical contrast-enhanced CTA was performed. CTA data were reconstructed with maximum intensity projection (MIP). Each patient underwent selective arteriography of the cerebral vessels (as the gold standard). CTA (axial images and MIP reconstructions) and arteriography were evaluated separately and their diagnostic information was compared. RESULTS: In 14 of the 53 patients neither CTA nor angiography showed a vascular malformation. In the remaining 39 patients, angiography demonstrated a total of 51 aneurysms ranging in size from 3 mm to 16 mm. CTA missed one of these aneurysms, which was located at the internal carotid artery. 3-D CT reconstruction was slightly superior to arteriography in the demonstration of the neck, shape and direction of the aneurysms. Partial thrombosis of 3 aneurysms was demonstrated only by CTA. CONCLUSION: Although CTA cannot replace cerebral arteriography in the diagnostic work-up of acute SAH, it proved to be helpful in demonstrating the topographic anatomy of cerebral aneurysms and surrounding structures.

Acute Disease↗

PubMedDate not supplied

Diffusion-weighted imaging with calculated apparent diffusion coefficient in intracranial hemorrhagic lesions.

In the literature published so far, measurement of values of the apparent diffusion coefficient (ADC) using an echo-planar imaging (EPI) technique in intracranial hemorrhagic lesions show no uniform results. Furthermore, no data exist for bleedings into intracranial lesions. We investigated the ADCs of 18 intracranial hemorrhagic lesions of different stages using echo-planar diffusion-weighted imaging (DWI). The ADC values measured in the hemorrhagic lesions ranged from 1.42 x 10(-3) to 0.22 x 10(-3) mm(2)/s. There were no significant differences between the ADC values in the hemorrhagic lesions and the contralateral white matter (P=.39). A differentiation between the lesions only with the ADC value was not possible as well. Using EPI DWI in intracranial hemorrhagic lesions of different stages, no reliable ADC values were found and a dependable differentiation between the lesions is not possible.

Adult↗

PubMedDate not supplied

The quality of functional MR images in patients with brain tumors: influences of neurological disorders and tumor location.

The aim of our study was to investigate the influence of neurological disorders, and the influence of tumor and perifocal edema location on functional magnetic resonance imaging (fMRI) quality. fMRI quality tended to be better the closer the tumor and the perifocal edema were located to the pmc. Hemipareses and seizures had no significant influence on fMRI quality. Therefore, hemiparetic patients do not have to be excluded beforehand. The evaluation of time courses is essential before using z-maps to localize eloquent brain regions preoperatively.

Adult↗